As a cooling device of a linear motor for driving a vehicle, there is a cooling device configured, for example, in such a manner that the coil of the linear motor is covered with a duct and the coil is cooled by letting a current of cooling air through the duct. According to this cooling device, the duct is divided into two parts along the longitudinal direction and one is used as a cooling portion in which the coil is accommodated and cooled and the other is used as a ventilation portion through which a current of cooling air from the blower is forced. A plurality of continuous holes are provided between the cooling portion and the ventilation portion along the longitudinal direction of the duct (see Patent Document 1).
Because the linear motor main body is of an elongate structure as a whole, so is the duct that covers the coil. Accordingly, it is configured in such a manner that the hole diameter of the continuous holes is made larger with an increasing distance from right beside the blower for forcing a current of cooling air inside the ventilation portion into the cooling portion at an almost uniform pressure along the longitudinal direction of the duct, so that the entire coil is cooled homogeneously.    Patent Document 1: JP-A-64-34105 (page 1 and FIG. 1 through FIG. 3)